Our main objective is to define the precise sequence of events that occur during the formation of a nerve-muscle synapse. Dissociated cell cultures derived from embryonic muscle, spinal cord, ciliary ganglia and sensory ganglia are explored with microelectrode, electron microscopic, autoradiographic and biochemical techniques. The focus is on early parameters of transmitter (ACh) release, on the clustering of ACh receptors in the postsynaptic membrane and on the accumulation of synaptic acetylcholinesterase. We will also study effects of nerve-muscle activity and of soluble factors derived from CNS tissue on the formation and subsequent maturation of functional contacts. In order to generalize results obtained at neuromuscular junctions to interneuronal contacts, we will first identify and characterize GABAnergic inhibitory synapses in spinal cord cell cultures and in spinal cord/sensory ganglion cocultures.